1. Field of the Invention
The present invention relates to an optical measuring apparatus.
2. Description of Related Art
Conventionally, a scanning optical measuring apparatus is known in which laser beams bombard a measured object (work piece) by scanning in parallel, then a dimension of the work piece is measured from a pattern of light and dark (scan signal) in a scan direction, which is detected from behind the work piece. As an example of the above-noted optical measuring apparatus, a device is known which is capable of correcting misalignment in a direction orthogonal to the scan direction (see, e.g., Japanese Patent Laid-open Publication No. 2010-249604). In addition, a device is known which is capable of recognizing a valid measurement range and of achieving highly accurate measurement (see, e.g., Japanese Patent Laid-open Publication No. 2011-106817).
However, the technologies disclosed by Japanese Patent Laid-open Publication Nos. 2010-249604 and 2011-106817 are not capable of eliminating an adverse influence of outside light (skip light) reflecting off the work piece. In particular, as shown in FIG. 8, in a case where a surface of a work piece W is nearly a mirror surface, as in a pin gage, a portion of a laser beam 101, which is normally expected to be blocked by the work piece W, may reflect off a surface of the work piece W to become skip light L102 and strike a photoreceiver element 132. In a case where the skip light L102 strikes the photoreceiver element 132, an amount of time that the work piece W blocks the laser beam L101 is shorter in comparison to a case where the skip light L102 does not strike the photoreceiver element 132. The conventional optical measuring apparatus measures a dimension based on an amount of time that the laser beam L101 is blocked. Therefore, when the amount of time is shorter, a dimension is measured that is correspondingly smaller than an actual dimension of the work piece W.
The present invention provides an optical measuring apparatus capable of accurately measuring a dimension of a measured object.